1. Field of the Invention
The present invention relates to the mapping of color images to black-and-white images and, more particularly, to the mapping of color images to black-and-white textured images comprising texture patterns which vary smoothly over color space.
2. Description of the Related Art
As the creation and display of computer-generated colored images continues to grow, methods for printing these images become increasingly important. While printing in full color may give the best rendition of a colored image, for reasons of availability, cost or speed of printing, one may sometimes choose to print the image on a black-and-white device. When a black-and-white device is used, some mapping must be employed to reduce the colors in the original image to those which the printer can produce. Typically, this is done by first mapping the full color image to a gray level image. The luminance of each pixel in the original image is usually used as the value for the corresponding gray level pixel. This is the mapping which occurs in black-and-white photographs and in black-and-white television. For pictorial images, most of the information is in the luminance channel, and this mapping works quite well. A black-and-white printer would next apply a halftone to the gray level image to yield a pattern of black-and-white dots which appear gray when viewed from a distance. The halftone patterns are designed to minimize the appearance of textures from the halftone screen. Again, this works well for pictorial images where one is interested in the apparent gray level of a point and not the method used to create it.
Many computer-generated colored images, however, such as those arising from business or presentation graphics, use color in a manner different than that used in pictorial images. In these images, the colors chosen are usually bright and highly saturated for maximum visual impact. Colors are differentiated primarily by hue. For these images, the mapping to luminance is much less appropriate. Information lies in the hue rather than the luminance, and while light colors look light, and dark colors look dark, very different colors (e.g. light blue and green) can have the same luminance and be indistinguishable when mapped to a gray level.
One solution to this, when there are a few specific colors, has been to select a corresponding set of texture patterns and to replace each color by a given texture. This solution is limited to only those colors for which texture patterns have been designed.
The related art describes mapping of color images to black-and-white images.
U.S. Pat. Nos. 4,688,031 and 4,703,318 to Haggerty disclose systems for transforming a color image to a monochromatic image having a particular pattern of light and dark dots which correspond to the original color of an area of the image. The dot patterns provide differing textural appearance for each color. Transformation of a color image to a monochromatic image is performed by replacing each area of the color image with a monochromatic dot pattern corresponding to a color pattern mask.
U.S. Pat. No. 4,225,861 to Langdon, Jr. et al discloses a method and apparatus for displaying texture in color patterns of a raster scanned display surface.
U.S. Pat. No. 4,741,046 to Matsunawa et al discloses a method of discriminating pictures wherein a texture of an image block is used to sort out similar image blocks. Once sorted, the blocks can be extracted from the image. A background pixel is determined using thresholding.
U.S. Pat. No. 4,888,713 to Falk discloses a surface detailed mapping system wherein textures are used to create a more realistic three-dimensional image on a two-dimensional display. A texture can be stored in memory and then used at a later date.
While the related art recognizes that color images can be mapped to black-and-white images using textured patterns, the art does not recognize that any color in the three-dimensional space can be mapped to a distinct texture on a pixel-by-pixel basis.